1. Field of the Invention
This invention relates to a radiation image recording and read-out method and apparatus, wherein a radiation image is stored on a stimulable phosphor sheet, the stimulable phosphor sheet, on which the radiation image has been stored, is exposed to stimulating rays, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to radiation, the emitted light is detected, and the radiation image is thereby read out from the stimulable phosphor sheet.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected with read-out means, such as a photomultiplier, and converted into an electric image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material.
The applicant proposed built-in types of radiation image recording and read-out apparatuses, comprising: (i) circulation and conveyance means for conveying at least one stimulable phosphor sheet along a circulation path, (ii) an image recording section, which is located in the circulation path and in which a radiation image of an object is stored on the stimulable phosphor sheet, (iii) an image read-out section, which is located in the circulation path and in which the radiation image is read out from the stimulable phosphor sheet, and (iv) an erasing section, which is located in the circulation path and in which energy remaining on the stimulable phosphor sheet after the radiation image has been read out therefrom is released. The built-in types of radiation image recording and read-out apparatuses are disclosed in, for example, U.S. Pat. Nos. 4,543,479 and 4,851,679, and Japanese Unexamined Patent Publication No. 3(1991)-238441. With the proposed built-in types of radiation image recording and read-out apparatuses, the stimulable phosphor sheet is utilized repeatedly and is processed efficiently.
Also, as a different example of the built-in type of radiation image recording and read-out apparatus, there has heretofore been known a radiation image recording and read-out apparatus, wherein a stimulable phosphor sheet is kept stationary, and a read-out unit, which comprises a stimulating ray source and photoelectric read-out means, is reciprocally moved with respect to the stimulable phosphor sheet. In this manner, image readout is performed. Further, a radiation image recording and read-out apparatus has been known, wherein a read-out unit is combined with an erasing section to constitute a read-out and erasing unit, and the read-out and erasing unit is reciprocally moved with respect to a stimulable phosphor sheet. Also, a radiation image read-out operation is performed in the course of forward movement of the read-out and erasing unit, and an erasing operation for releasing energy remaining on the stimulable phosphor sheet is performed in the course of backward movement of the read-out and erasing unit. Such radiation image recording and read-out apparatuses are proposed in, for example, Japanese Unexamined Patent Publication Nos. 58(1983)-200269 and 63(1988)-189855.
When a stimulable phosphor sheet, on which a radiation image has been stored, is exposed to stimulating rays, the stimulable phosphor sheet is caused by the stimulating rays to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. When a stimulable phosphor sheet is exposed to radiation carrying image information of an object, instantaneous light emission occurs with the stimulable phosphor sheet simultaneously with its exposure to the radiation. The instantaneous light emission continues for a certain length of time after the exposure of the stimulable phosphor sheet to the radiation is ceased, while the intensity of the instantaneously emitted light is decreasing little by little. The instantaneous light emission is referred to as the xe2x80x9cradiation after-glow.xe2x80x9d If the radiation image read-out operation is performed to obtain an image signal representing the radiation image in the state in which the radiation after-glow remains, noise due to the radiation after-glow will occur on the image signal. Therefore, contrast of a visible image reproduced from the image signal will become low, and a radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, cannot be obtained.
In order for the aforesaid problems to be eliminated, a radiation image read-out apparatus has been proposed, wherein the characteristics such that the radiation after-glow reduces sharply with heat are utilized, and wherein a radiation image read-out operation is performed after a stimulable phosphor sheet, on which a radiation image has been stored, is exposed to heat. The radiation image read-out apparatus is disclosed in, for example, Japanese Unexamined Patent Publication No. 8(1996)-87084.
However, with the radiation image read-out apparatus proposed in Japanese Unexamined Patent Publication No. 8(1996)-87084, it is necessary for the apparatus to be provided with heating means for heating the stimulable phosphor sheet. Also, it is necessary for means for cooling the regions around the heating means, or the like, to be provided such that other means in the radiation image read-out apparatus may not be adversely affected by heat. Therefore, the proposed radiation image read-out apparatus cannot be kept small in size.
The primary object of the present invention is to provide a radiation image recording and read-out method, wherein adverse effects of radiation after-glow are capable of being reduced with a simple constitution.
Another object of the present invention is to provide an apparatus for carrying out the radiation image recording and read-out method.
The present invention provides a radiation image recording and read-out method, comprising the steps of:
i) exposing a stimulable phosphor sheet, which is capable of storing a radiation image thereon, to radiation carrying image information of an object in order to store a radiation image of the object on the stimulable phosphor sheet,
ii) exposing the stimulable phosphor sheet, on which the radiation image has been stored, to stimulating rays, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation, and photoelectrically detecting the emitted light with photoelectric read-out means in order to read out the radiation image,
iii) releasing energy, which remains on the stimulable phosphor sheet after the radiation image has been read out therefrom, before a next radiation image is stored on the stimulable phosphor sheet, and
iv) moving the stimulable phosphor sheet with respect to at least an image read-out section, in which the step of reading out the radiation image is performed,
wherein the improvement comprises the steps of:
a) setting a waiting time between when the radiation image was stored on the stimulable phosphor sheet and when the readout of the radiation image from the stimulable phosphor sheet is begun, the waiting time being set in accordance with an intensity of radiation afterglow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet, and
b) controlling the step of reading out the radiation image and the step of moving the stimulable phosphor sheet with respect to the image read-out section, such that the readout of the radiation image from the stimulable phosphor sheet is begun after the waiting time, which has been set, has elapsed.
In the radiation image recording and read-out method in accordance with the present invention, the intensity of the radiation after-glow may be found by directly detecting the radiation after-glow occurring with the stimulable phosphor sheet. Alternatively, the intensity of the radiation after-glow may be calculated in accordance with radiation after-glow characteristics of the stimulable phosphor sheet, a radiation dose delivered at the time of the recording of the radiation image, a tube voltage of a radiation source, information representing the time of image recording, and the like.
As will be understood from the specification, it should be noted that the term xe2x80x9cmoving a stimulable phosphor sheet with respect to an image read-out sectionxe2x80x9d as used herein means movement of the stimulable phosphor sheet relative to the image read-out section, and embraces both the cases wherein the stimulable phosphor sheet is moved while the image read-out section is kept stationary, and cases wherein the image read-out section is moved while the stimulable phosphor sheet is kept stationary.
Also, the radiation image recording and readout method in accordance with the present invention may be modified such that the step of moving the stimulable phosphor sheet with respect to at least the image read-out section is a step of conveying the stimulable phosphor sheet along a predetermined circulation path, which passes through the step of storing the radiation image of the object on the stimulable phosphor sheet, the step of reading out the radiation image, and the step of releasing energy remaining on the stimulable phosphor sheet.
Further, the radiation image recording and read-out method in accordance with the present invention may be modified such that the step of reading out the radiation image is performed within a read-out unit, and
the step of moving the stimulable phosphor sheet with respect to at least the image read-out section is a step of reciprocally moving the read-out unit with respect to the stimulable phosphor sheet.
Further, the radiation image recording and read-out method in accordance with the present invention should preferably be modified such that the method further comprises the step of detecting the intensity of the radiation after-glow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet, and
the waiting time is set in accordance with the intensity of the radiation after-glow, which has been detected.
In such cases, the detection of the intensity of the radiation after-glow should preferably be performed with comparatively simple detection means, such as a line sensor.
Furthermore, in the radiation image recording and read-out method in accordance with the present invention, the photoelectric read-out means should preferably also perform the detection of the intensity of the radiation after-glow.
In cases where the photoelectric read-out means also performs the detection of the intensity of the radiation after-glow, the detection should preferably be performed without the stimulating rays being irradiated to the stimulable phosphor sheet.
Also, in the radiation image recording and read-out method in accordance with the present invention, the movement of the stimulable phosphor sheet should preferably be controlled such that, when the radiation after-glow is to be detected, the stimulable phosphor sheet is moved more quickly than when the radiation image is read out from the stimulable phosphor sheet.
Further, in the radiation image recording and read-out method in accordance with the present invention, the photoelectric read-out means may be constituted of a line sensor comprising a plurality of photoelectric conversion devices arrayed in a direction approximately normal to a direction, along which the stimulable phosphor sheet is moved.
The present invention also provides an apparatus for carrying out the radiation image recording and read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image recording and read-out apparatus, comprising:
i) an image recording section for exposing a stimulable phosphor sheet, which is capable of storing a radiation image thereon, to radiation carrying image information of an object in order to store a radiation image of the object on the stimulable phosphor sheet,
ii) an image read-out section provided with:
a stimulating ray source for producing stimulating rays and irradiating the stimulating rays to the stimulable phosphor sheet, on which the radiation image has been stored in the image recording section, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation, and
photoelectric read-out means for photoelectrically detecting the emitted light in order to read out the radiation image,
iii) an erasing section for releasing energy, which remains on the stimulable phosphor sheet after the radiation image has been read out therefrom, before a next radiation image is stored on the stimulable phosphor sheet, and
iv) conveyance means for moving the stimulable phosphor sheet with respect to at least the image readout section,
wherein the improvement comprises the provision of:
a) setting means for setting a waiting time between when the radiation image was stored on the stimulable phosphor sheet and when the readout of the radiation image from the stimulable phosphor sheet is begun, the waiting time being set in accordance with an intensity of radiation after-glow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet, and
b) control means for controlling the image read-out section and the conveyance means, such that the readout of the radiation image from the stimulable phosphor sheet in the image read-out section is begun after the waiting time, which has been set by the setting means, has elapsed.
In the radiation image recording and read-out apparatus in accordance with the present invention, the conveyance means may be means for conveying the stimulable phosphor sheet along a predetermined circulation path, which passes through the image recording section, the image read-out section, and the erasing section.
Also, the radiation image recording and readout apparatus in accordance with the present invention may be modified such that the image read-out section is unitized to constitute a read-out unit, and
the conveyance means is means for reciprocally moving the read-out unit with respect to the stimulable phosphor sheet.
Further, the radiation image recording and read-out apparatus in accordance with the present invention should preferably be modified such that the apparatus further comprises detection means for detecting the intensity of the radiation after-glow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet, and
the setting means sets the waiting time in accordance with the intensity of the radiation after-glow, which has been detected by the detection means.
In such cases, as the detection means, comparatively simple detection means, such as a line sensor, should preferably be employed.
Furthermore, in the radiation image recording and read-out apparatus in accordance with the present invention, the photoelectric read-out means should preferably also act as the detection means.
In cases where the photoelectric read-out means also acts as the detection means, the detection should preferably be performed without the stimulating rays being irradiated to the stimulable phosphor sheet.
Also, in the radiation image recording and read-out apparatus in accordance with the present invention, the control means should preferably control the conveyance means such that, when the radiation after-glow is to be detected, the stimulable phosphor sheet is conveyed more quickly than when the radiation image is read out from the stimulable phosphor sheet.
Further, in the radiation image recording and read-out apparatus in accordance with the present invention, the photoelectric read-out means may be constituted of a line sensor comprising a plurality of photoelectric conversion devices arrayed in a direction approximately normal to a direction, along which the stimulable phosphor sheet is conveyed.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, the waiting time between when the radiation image was stored on the stimulable phosphor sheet and when the readout of the radiation image from the stimulable phosphor sheet is begun is set in accordance with the intensity of the radiation after-glow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet. Also, when the waiting time, which has been set, has elapsed after the image recording operation was finished, the readout of the radiation image from the stimulable phosphor sheet is begun. Therefore, large-scaled means, such as heating means, need not be provided, and the readout of the radiation image from the stimulable phosphor sheet can be performed without being adversely affected by the radiation after-glow. Accordingly, an image signal free from noise due to the radiation after-glow can be obtained.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, wherein the detection means for detecting the intensity of the radiation after-glow is provided, the intensity of the radiation after-glow, which continues to occur with the stimulable phosphor sheet after the radiation image was stored on the stimulable phosphor sheet, can be detected accurately. Therefore,the waiting time can be set accurately, and the operation for reading out the radiation image can be performed efficiently.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, wherein the photoelectric read-out means also acts as the detection means, the detection of the intensity of the radiation after-glow can be performed without particular means being utilized. Therefore, the radiation image recording and read-out apparatus can be kept small in size.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, the conveyance of the stimulable phosphor sheet may be controlled such that, when the radiation after-glow is to be detected, the stimulable phosphor sheet is conveyed more quickly than when the radiation image is read out from the stimulable phosphor sheet. In such cases, the detection of the intensity of the radiation after-glow can be performed quickly, and therefore the operation for reading out the radiation image can be performed efficiently.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, wherein the photoelectric read-out means is constituted of the line sensor comprising a plurality of photoelectric conversion devices, the size of the image read-out section and the size of the radiation image recording and read-out apparatus can be kept small.